mojo/system/dispatcher.h

// Copyright 2013 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#ifndef MOJO_SYSTEM_DISPATCHER_H_
#define MOJO_SYSTEM_DISPATCHER_H_

#include <stddef.h>
#include <stdint.h>

#include <vector>

#include "base/macros.h"
#include "base/memory/ref_counted.h"
#include "base/synchronization/lock.h"
#include "mojo/public/system/core.h"
#include "mojo/system/system_impl_export.h"

namespace mojo {
namespace system {

class Channel;
class CoreImpl;
class Dispatcher;
class DispatcherTransport;
class LocalMessagePipeEndpoint;
class MessageInTransit;
class ProxyMessagePipeEndpoint;
class Waiter;

namespace test {

// Test helper. We need to declare it here so we can friend it.
MOJO_SYSTEM_IMPL_EXPORT DispatcherTransport DispatcherTryStartTransport(
    Dispatcher* dispatcher);

}  // namespace test

// A |Dispatcher| implements Mojo primitives that are "attached" to a particular
// handle. This includes most (all?) primitives except for |MojoWait...()|. This
// object is thread-safe, with its state being protected by a single lock
// |lock_|, which is also made available to implementation subclasses (via the
// |lock()| method).
class MOJO_SYSTEM_IMPL_EXPORT Dispatcher :
    public base::RefCountedThreadSafe<Dispatcher> {
 public:
  enum Type {
    kTypeUnknown = 0,
    kTypeMessagePipe,
    kTypeDataPipeProducer,
    kTypeDataPipeConsumer
  };
  virtual Type GetType() const = 0;

  // These methods implement the various primitives named |Mojo...()|. These
  // take |lock_| and handle races with |Close()|. Then they call out to
  // subclasses' |...ImplNoLock()| methods (still under |lock_|), which actually
  // implement the primitives.
  // NOTE(vtl): This puts a big lock around each dispatcher (i.e., handle), and
  // prevents the various |...ImplNoLock()|s from releasing the lock as soon as
  // possible. If this becomes an issue, we can rethink this.
  MojoResult Close();

  // |transports| may be non-null if and only if there are handles to be
  // written; not that |this| must not be in |transports|. On success, all the
  // dispatchers in |transports| must have been moved to a closed state; on
  // failure, they should remain in their original state.
  MojoResult WriteMessage(const void* bytes,
                          uint32_t num_bytes,
                          std::vector<DispatcherTransport>* transports,
                          MojoWriteMessageFlags flags);
  // |dispatchers| must be non-null but empty, if |num_dispatchers| is non-null
  // and nonzero. On success, it will be set to the dispatchers to be received
  // (and assigned handles) as part of the message.
  MojoResult ReadMessage(
      void* bytes,
      uint32_t* num_bytes,
      std::vector<scoped_refptr<Dispatcher> >* dispatchers,
      uint32_t* num_dispatchers,
      MojoReadMessageFlags flags);
  MojoResult WriteData(const void* elements,
                       uint32_t* elements_num_bytes,
                       MojoWriteDataFlags flags);
  MojoResult BeginWriteData(void** buffer,
                            uint32_t* buffer_num_bytes,
                            MojoWriteDataFlags flags);
  MojoResult EndWriteData(uint32_t num_bytes_written);
  MojoResult ReadData(void* elements,
                      uint32_t* num_bytes,
                      MojoReadDataFlags flags);
  MojoResult BeginReadData(const void** buffer,
                           uint32_t* buffer_num_bytes,
                           MojoReadDataFlags flags);
  MojoResult EndReadData(uint32_t num_bytes_read);
  // |options| may be null. |new_dispatcher| must not be null, but
  // |*new_dispatcher| should be null (and will contain the dispatcher for the
  // new handle on success).
  MojoResult DuplicateBufferHandle(
      const MojoDuplicateBufferHandleOptions* options,
      scoped_refptr<Dispatcher>* new_dispatcher);
  MojoResult MapBuffer(uint64_t offset,
                       uint64_t num_bytes,
                       void** buffer,
                       MojoMapBufferFlags flags);

  // Adds a waiter to this dispatcher. The waiter will be woken up when this
  // object changes state to satisfy |flags| with result |wake_result| (which
  // must be >= 0, i.e., a success status). It will also be woken up when it
  // becomes impossible for the object to ever satisfy |flags| with a suitable
  // error status.
  //
  // Returns:
  //  - |MOJO_RESULT_OK| if the waiter was added;
  //  - |MOJO_RESULT_ALREADY_EXISTS| if |flags| is already satisfied;
  //  - |MOJO_RESULT_INVALID_ARGUMENT| if the dispatcher has been closed; and
  //  - |MOJO_RESULT_FAILED_PRECONDITION| if it is not (or no longer) possible
  //    that |flags| will ever be satisfied.
  MojoResult AddWaiter(Waiter* waiter,
                       MojoWaitFlags flags,
                       MojoResult wake_result);
  void RemoveWaiter(Waiter* waiter);

  // A dispatcher must be put into a special state in order to be sent across a
  // message pipe. Outside of tests, only |CoreImplAccess| is allowed to do
  // this, since there are requirements on the handle table (see below).
  //
  // In this special state, only a restricted set of operations is allowed.
  // These are the ones available as |DispatcherTransport| methods. Other
  // |Dispatcher| methods must not be called until |DispatcherTransport::End()|
  // has been called.
  class CoreImplAccess {
   private:
    friend class CoreImpl;
    // Tests also need this, to avoid needing |CoreImpl|.
    friend DispatcherTransport test::DispatcherTryStartTransport(Dispatcher*);

    // This must be called under the handle table lock and only if the handle
    // table entry is not marked busy. The caller must maintain a reference to
    // |dispatcher| until |DispatcherTransport::End()| is called.
    static DispatcherTransport TryStartTransport(Dispatcher* dispatcher);
  };

  // A |MessageInTransit| may serialize dispatchers that are attached to it to a
  // given |Channel| and then (probably in a different process) deserialize.
  // TODO(vtl): Consider making another wrapper similar to |DispatcherTransport|
  // (but with an owning, unique reference), and having
  // |CreateEquivalentDispatcherAndCloseImplNoLock()| return that wrapper (and
  // |MessageInTransit| only holding on to such wrappers).
  class MessageInTransitAccess {
   private:
    friend class MessageInTransit;

    // Serialization API. These functions may only be called on such
    // dispatchers. (|channel| is the |Channel| to which the dispatcher is to be
    // serialized.) See the |Dispatcher| methods of the same names for more
    // details.
    // TODO(vtl): Consider replacing this API below with a proper two-phase one
    // ("StartSerialize()" and "EndSerializeAndClose()", with the lock possibly
    // being held across their invocations).
    static size_t GetMaximumSerializedSize(const Dispatcher* dispatcher,
                                           const Channel* channel);
    static bool SerializeAndClose(Dispatcher* dispatcher,
                                  Channel* channel,
                                  void* destination,
                                  size_t* actual_size);

    // Deserialization API.
    // TODO(vtl): Implement this.
    static scoped_refptr<Dispatcher> Deserialize(Channel* channel,
                                                 int32_t type,
                                                 const void* source,
                                                 size_t size);
  };

 protected:
  Dispatcher();

  friend class base::RefCountedThreadSafe<Dispatcher>;
  virtual ~Dispatcher();

  // These are to be overridden by subclasses (if necessary). They are called
  // exactly once -- first |CancelAllWaitersNoLock()|, then |CloseImplNoLock()|,
  // when the dispatcher is being closed. They are called under |lock_|.
  virtual void CancelAllWaitersNoLock();
  virtual void CloseImplNoLock();
  virtual scoped_refptr<Dispatcher>
      CreateEquivalentDispatcherAndCloseImplNoLock() = 0;

  // These are to be overridden by subclasses (if necessary). They are never
  // called after the dispatcher has been closed. They are called under |lock_|.
  // See the descriptions of the methods without the "ImplNoLock" for more
  // information.
  virtual MojoResult WriteMessageImplNoLock(
      const void* bytes,
      uint32_t num_bytes,
      std::vector<DispatcherTransport>* transports,
      MojoWriteMessageFlags flags);
  virtual MojoResult ReadMessageImplNoLock(
      void* bytes,
      uint32_t* num_bytes,
      std::vector<scoped_refptr<Dispatcher> >* dispatchers,
      uint32_t* num_dispatchers,
      MojoReadMessageFlags flags);
  virtual MojoResult WriteDataImplNoLock(const void* elements,
                                         uint32_t* num_bytes,
                                         MojoWriteDataFlags flags);
  virtual MojoResult BeginWriteDataImplNoLock(void** buffer,
                                              uint32_t* buffer_num_bytes,
                                              MojoWriteDataFlags flags);
  virtual MojoResult EndWriteDataImplNoLock(uint32_t num_bytes_written);
  virtual MojoResult ReadDataImplNoLock(void* elements,
                                        uint32_t* num_bytes,
                                        MojoReadDataFlags flags);
  virtual MojoResult BeginReadDataImplNoLock(const void** buffer,
                                             uint32_t* buffer_num_bytes,
                                             MojoReadDataFlags flags);
  virtual MojoResult EndReadDataImplNoLock(uint32_t num_bytes_read);
  virtual MojoResult DuplicateBufferHandleImplNoLock(
      const MojoDuplicateBufferHandleOptions* options,
      scoped_refptr<Dispatcher>* new_dispatcher);
  virtual MojoResult MapBufferImplNoLock(uint64_t offset,
                                         uint64_t num_bytes,
                                         void** buffer,
                                         MojoMapBufferFlags flags);
  virtual MojoResult AddWaiterImplNoLock(Waiter* waiter,
                                         MojoWaitFlags flags,
                                         MojoResult wake_result);
  virtual void RemoveWaiterImplNoLock(Waiter* waiter);

  // These implement the API used to serialize dispatchers to a |Channel|
  // (described below). They will only be called on a dispatcher that's attached
  // to and "owned" by a |MessageInTransit|. See the non-"impl" versions for
  // more information.
  // TODO(vtl): Consider making these pure virtual once most things support
  // being passed over a message pipe.
  virtual size_t GetMaximumSerializedSizeImplNoLock(
      const Channel* channel) const;
  virtual bool SerializeAndCloseImplNoLock(Channel* channel,
                                           void* destination,
                                           size_t* actual_size);

  // Available to subclasses. (Note: Returns a non-const reference, just like
  // |base::AutoLock|'s constructor takes a non-const reference.)
  base::Lock& lock() const { return lock_; }

 private:
  friend class DispatcherTransport;

  // This should be overridden to return true if/when there's an ongoing
  // operation (e.g., two-phase read/writes on data pipes) that should prevent a
  // handle from being sent over a message pipe (with status "busy").
  virtual bool IsBusyNoLock() const;

  // Closes the dispatcher. This must be done under lock, and unlike |Close()|,
  // the dispatcher must not be closed already. (This is the "equivalent" of
  // |CreateEquivalentDispatcherAndCloseNoLock()|, for situations where the
  // dispatcher must be disposed of instead of "transferred".)
  void CloseNoLock();

  // Creates an equivalent dispatcher -- representing the same resource as this
  // dispatcher -- and close (i.e., disable) this dispatcher. I.e., this
  // dispatcher will look as though it was closed, but the resource it
  // represents will be assigned to the new dispatcher. This must be called
  // under the dispatcher's lock.
  scoped_refptr<Dispatcher> CreateEquivalentDispatcherAndCloseNoLock();

  // API to serialize dispatchers to a |Channel|, exposed to only
  // |MessageInTransit| (via |MessageInTransitAccess|). They may only be called
  // on a dispatcher attached to a |MessageInTransit| (and in particular not in
  // |CoreImpl|'s handle table).
  // Gets the maximum amount of space that'll be needed to serialize this
  // dispatcher to the given |Channel|. Returns zero to indicate that this
  // dispatcher cannot be serialized (to the given |Channel|).
  size_t GetMaximumSerializedSize(const Channel* channel) const;
  // Serializes this dispatcher to the given |Channel| by writing to
  // |destination| and then closes this dispatcher. It may write no more than
  // was indicated by |GetMaximumSerializedSize()|. (WARNING: Beware of races,
  // e.g., if something can be mutated between the two calls!) Returns true on
  // success, in which case |*actual_size| is set to the amount it actually
  // wrote to |destination|. On failure, |*actual_size| should not be modified;
  // however, the dispatcher will still be closed.
  bool SerializeAndClose(Channel* channel,
                         void* destination,
                         size_t* actual_size);

  // This protects the following members as well as any state added by
  // subclasses.
  mutable base::Lock lock_;
  bool is_closed_;

  DISALLOW_COPY_AND_ASSIGN(Dispatcher);
};

// Wrapper around a |Dispatcher| pointer, while it's being processed to be
// passed in a message pipe. See the comment about |Dispatcher::CoreImplAccess|
// for more details.
//
// Note: This class is deliberately "thin" -- no more expensive than a
// |Dispatcher*|.
class MOJO_SYSTEM_IMPL_EXPORT DispatcherTransport {
 public:
  DispatcherTransport() : dispatcher_(NULL) {}

  void End();

  Dispatcher::Type GetType() const { return dispatcher_->GetType(); }
  bool IsBusy() const { return dispatcher_->IsBusyNoLock(); }
  void Close() { dispatcher_->CloseNoLock(); }
  scoped_refptr<Dispatcher> CreateEquivalentDispatcherAndClose() {
    return dispatcher_->CreateEquivalentDispatcherAndCloseNoLock();
  }

  bool is_valid() const { return !!dispatcher_; }

 protected:
  Dispatcher* dispatcher() { return dispatcher_; }

 private:
  friend class Dispatcher::CoreImplAccess;

  explicit DispatcherTransport(Dispatcher* dispatcher)
      : dispatcher_(dispatcher) {}

  Dispatcher* dispatcher_;

  // Copy and assign allowed.
};

}  // namespace system
}  // namespace mojo

#endif  // MOJO_SYSTEM_DISPATCHER_H_